Special purpose hearing aid



July 23, 1968 n. E. ANDREWS, JR 3,394,226

SPECIAL PURPOSE HEARING AID Filed Aug. 19, 1963 FIG. 3

A B 4 l REJECTION FILTERS DC SUPPLY ACCEPTANCE TUNED FILTERS P DETECTOR 402 405 A B REJECTION swncums M FILTER CIRCUIT INVENTOR.

F, 6 4 DAN/EL E. ANDREW-S, JR.

AL? 5% I 44 n A [av sis United States Patent Ofi ice 3,394,226 Patented July 23, 1968 The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a special purpose hearing aid and particularly, to a hearing aid for use in high level noise environments and specifically, to a hearing aid which will selectively filter out high level noise and allow persons wearing the system to communicate at ordinary and normal levels.

In the past when working conditions have required the exposure of personnel to high intensity sound (especially when this sound is characteristically limited to narrow bands of frequency), it has been normal practice to run audiograms at regular intervals on the personnel involved to measure their hearing abilities and any changes therein. As soon as a persons hearing shows any signs of deterioration, that person is removed from the noisy environment. Another way of coping with high level sound is to provide ear defenders; however, the ear defenders cut out normal noise and conversation as Well (i.e., the ear defenders attenuate the acoustic energy from all bands of frequencies more or less uniformly). Devices which attenuate high intensity sound without attenuating normal noise and conversation have not had practical application as of yet.

An object of the present invention is to provide a practical hearing aid for use in the presence of high-level narrow bands of acoustic energy.

A further object of the present invention is to provide a practical hearing aid for use in the presence of highlevel narrow bands of acoustic energy, through which the intelligibility of sound outside the bands of acoustic energy is maintained.

A further object of the present invention is to provide a practical hearing aid which prevents aural system deterioration arising from exposure to intense or high-level sound.

Other objects and many of the attendant advantages of this invention will be readily appreciated as they become better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates the system in position on a users head;

FIG. 2 illustrates a proposed positioning of the components of the system;

FIG. 3 illustrates one embodiment of the invention;

FIG. 4 illustrates another embodiment of the invention.

FIG. 1 illustrates the system in position on a users head, which system comprises for example earmutfs 100, 101 and supporting band 102 which is used to hold the muffs securely over the ears of the user. It is proposed that the system be binaural in order to preserve the directivity aspects incident to a binaural system. The ear muffs 100 and 101 are of such a nature that substantially all sound emanating outside the ear muffs is prevented from reaching the users cars. It is to be understood that the use of muffs is merely exemplary and that car appliances and/or a helmet-like appliance or any other type of apparatus that will prevent the wearers hearing outside airborne sound might be used in the invention.

FIG. 2 illustrates the placement of the electronics and microphone and earphone with respect to the mufis 101 and 100. Again, it is to be understood that the showing is merely exemplary and that there are many ways in which the placement of the electronics in the system may be implemented.

FIG. 3 illustrates an embodiment of the invention which is particularly adapted for use in a noisy or highlevel noise environment wherein the high level noise is substantially continuous (i.e., the system still maintains its communication effectiveness with adequate aural protection even though the bands of noise are present a high percent of the time). In such a system a sound barrier may be placed at any point between A and B. This is a barrier to exclude virtually all outside airborne sound from the hearers ear. In such a system a microphone 300 is used to pick up outside airborne sound and the output of the microphone coupled to an amplifier 302. Coupled to the output of the amplifier 302 are rejection filters 303 which are chosen so that the appropriate narrow band of frequencies is rejected while all other frequencies outside the selected band (or bands) are passed. The output of the rejection filters is then coupled to an amplifier 304 and the output of the amplifier 304 introduced to the input of an earphone 301 Which in turn is adapted for positioning in close proximity to the users car. A DC supply 305 is used to supply the power for the amplifiers 302. and 304.

In the operation of the system set forth in FIG. 3 the output of the microphone 300 is coupled to the amplifier 302 and amplified in a conventional manner. The output of the amplifier 302 is then coupled to the input of the rejection filter or filters 303 which are tuned to reject the band or bands of audio frequencies which comprise the high level sound. The band of frequencies rejected is rather narrow (i.e., of the order of 400 cycles per second) so that normal conversation may be carried on in the presence of the high-level noise. The output 01 the filter 303 is then coupled to the amplifier 304 and then to the earphone 301 which reproduces the outside airborne sound minus the high level sound.

The embodiment set forth in FIG. 4 is particularly adapted for use in an environment wherein the unwantec' sound is not continuous in nature, such as in most sonal systems. Such a system would improve the intelligibility of the sound heard by the user during periods of noninterference 'by subjecting the sound which the user hear: to filtering only as temporarily required.

In the system of FIG. 4 the sound barrier again is placed at any point between A and 1B. A microphone 40( in communication with outside airborne sound is coupler to an amplifier 401. The output of the amplifier 401 i: coupled as an input to acceptance filters 402 and rejection filter or filters 403 and is also coupled on a bypas: audio line 408 as one input to a switching circuit 404 The output of the acceptance filters is coupled to a tuner detector 405 the output of which comprises a control sig nal for the switching circuit 404. In addition, the outpu of the rejection filter or filters 403 is coupled as anothe: input to the switching circuit 404. The output of thi switching circuit 404 is coupled to an amplifier 406 th output of which is reproduced in earphone 407. In thi embodiment also, the earphone is adapted to be posi tioned in close proximity to the users ear so that th outside airborne sound passed by the system will b4 heard by the listener.

In the operation of the system set forth in FIG. 4 the acceptance filters 402 are chosen to pass the band 0 frequencies containing the high level noise or a particula supersonic signal which is emitted every time the high level noise source is activated. The detector is tuned t the supersonic frequency or the noise frequency to be re jected and the output of the detector 405 is used as a control signal which activates the switching circuit 404 to switch either the output of rejection filters 403 or amplifier 401 to the input of amplifier 406 for amplification and ultimate use.

Thus, when the output of rejection filters 403 is coupled to the input of amplifier 406 the entire audio range minus a narrow band of high-level frequency or frequencies is passed. When the output of amplifier 401 is coupled to the input of amplifier 406 on line 408 the entire range of frequencies is utilized.

As stated, either the high-level noise may be used as the control signal for switching circuit 404 or a supersonic signal which is emitted coincidently with the activation of the high-level noise source. In either case the system is the same.

The advantages of the system over those known are that the system prevents deafness arising from exposure to high-level sounds and allows normal conversation to be carried on in the presence of the high-level sound which lies in a narrow band or bands of frequency. In addition, the unit is compact and light which means that :he unit will be used rather than laid aside as being too bulky and cumbersome.

Obviously many modifications and variations of the present invention are possible in the light of the above :eachings. It is, therefore, to be understood that within ;he scope of the appended claims the invention may be racticed otherwise than as specifically described.

What is claimed is:

1. A special purpose hearing aid for improved voice :ommunication in the presence of narrow-band, highevel noise within the essential voice frequency band :omprising:

means for receiving acoustic energy including said essential voice frequency bands;

means for transducing said acoustic energy to electrical signals;

means continuously responsive to electrical signal energy representative of atonal elements within .said narrow-band, high level noise for rejecting predetermined frequency bandwith portions of said essential voice frequency band,

said predetermined frequency bandwith portions being selected within a bandwidth substantially of the order of 500 cycles or less so as to preserve maximum voice communication intelligibility and continuity relative to the signal-to-noise patio developed by said noise within said essential voice frequency band;

means for amplifying the remainder of said electrical signals;

means for converting the amplified signals to commensurate acoustic signals; and

means for transmitting said acoustic signals for aural reception by a listening person,

said means including means for substantially excluding local, ambient sounds from said listening person.

2. A special purpose hearing aid as claimed in claim 1 wherein said means continuously responsive to electrical signal energy representative of atonal elements within said narrow-band, high level noise for rejecting predetermined frequency bandwidth portions of said essential voice frequency band comprises electrical filters adapted to substantially attenuate said predetermined frequency bandwith.

3. A special purpose hearing aid as claimed in claim 1 wherein said means for transmitting said acoustic signals includes means for supporting thereon said transducing, selective rejection, and amplifying means.

4. A special purpose hearing aid for improved voice communication in the presence of narrow-band, high level noise within the essential voice frequency band compriss;

means for receiving acoustic energy including said essential voice frequency band;

means for transducing said acoustic energy to electrical signals;

means for selectively rejecting portions of said electrical signals representative of said narrow-band, high level noise within said essential voice frequency band;

means for amplifying the remainder of said electrical signals;

a conductive path connected to bypass said means for selectively rejecting portions of said electrical signals representative of said narrow-band, high level noise;

switch means adapted to selectively connect said conductive path to said amplifying means;

means for converting the amplified signals to commensurate acoustic signals; and

means for transmitting said acoustic signals for oral reception by a listening person, said means including means for substantially excluding local ambient sounds from said listening person.

5. A special purpose hearing aid as claimed in claim 4 wherein said switch means is responsive to a predetermined signal for disconnecting said conductive path.

6. A special purpose hearing aid as claimed in claim 5 wherein said predetermined signal is part of said high level noise and is of a frequency outside said essential voice frequency band.

References Cited UNITED STATES PATENTS 2,449,971 9/1948 Andrews 1791 2,972,018 2/1961 Hawley 1791 2,866,848 12/1958 Fogel 1791 3,098,121 7/1963 Wadsworth 1791 3,174,100 3/1965 Orr.

KATHLEEN H. CLAFFY, Primary Examiner. A. H. GESS, Assistant Examiner. 

1. A SPECIAL PURPOSE HEARING AID FOR IMPROVED VOICE COMMUNICATION IN THE PRESENCE OF NARROW-BAND, HIGHLEVEL NOISE WITHIN THE ESSENTIAL VOICE FREQUENCY BAND COMPRISING: MEANS FOR RECEIVING ACOUSTIC ENERGY INCLUDING SAID ESSENTIAL VOICE FREQUENCY BANDS; MEANS FOR TRANSDUCING SAID ACOUSTIC ENERGY TO ELECTRICAL SIGNALS; MEANS CONTINUOUSLY RESPONSIVE TO ELECTRICAL SIGNAL ENERGY REPRESENTATIVE OF ATONAL ELEMENTS WITHIN SAID NARROW-BAND, HIGH LEVEL NOISE FOR REJECTING PREDETERMINED FREQUENCY BANDWITH PORTIONS OF SAID ESSENTIAL VOICE FREQUENCY BAND, SAID PREDETERMINED FREQUENCY BANDWITH PORTIONS BEING SELECTED WITHIN A BANDWITH SUBSTANTIALLY OF THE ORDER OF 500 CYCLES OR LESS SO AS TO PRESERVE MAXIMUM VOICE COMMUNICATION INTELLIGIBILITY AND CONTINUITY RELATIVE TO THE SIGNAL-TO-NOISE RATIO DEVELOPED BY SAID NOISE WITHIN SAID ESSENTIAL VOICE FREQUENCY BAND; MEANS FOR AMPLIFYING THE REMAINDER OF SAID ELECTRICAL SIGNALS; MEANS FOR CONVERTING THE AMPLIFIED SIGNALS TO COMMENSURATE ACOUSTIC SIGNALS; AND MEANS FOR TRANSMITTING SAID ACOUSTIC SIGNALS FOR AURAL RECEPTION BY A LISTENING PERSON, SAID MEANS INCLUDING MEANS FOR SUBSTANTIALLY EXCLUDING LOCAL, AMBIENT SOUNDS FROM SAID LISTENING PERSON. 